1. Field of the Invention
The present invention relates to a fastener for releasably fastening a face guard or visor to a helmet for motorcycle riders etc. and particularly to such a fastener which facilitates fastening and unfastening the face guard to the helmet and which is completely immune from accidental unfastening.
2. Description of the Prior Art
One typical fastener of the type described is disclosed in Japanese Patent Laid-open Publication No. 2-133603. The disclosed fastener comprises a plug holder having a plug mounted thereon so as to be capable of coming into and out of the plug holder; a bowl-shaped socket having a central hole and a resilient hollow cylindrical portion provided on one side of the socket and surrounding the central hole, the forward end of the plug being resiliently engageable with the resilient cylindrical portion of the socket; and a pusher including a circular base plate and a push rod protuberantly mounted on the middle thereof, the pusher reciprocally mounted on the other side of the socket with the push rod fit through the central hole. In order to couple the plug with the socket, a wearer presses the plug holder against the socket with the protruding plug registering with the hollow cylindrical portion until the plug comes into engagement with the resilient cylindrical portion of the socket. In order to decouple the plug holder from the socket, he must press the pusher against the socket until the pusher rod intrudes into the hollow cylindrical portion of the socket and pushes the plug out of engagement with the resilient cylindrical portion.
Another fastener of the type described is disclosed in Japanese Utility Model Laid-open Publication No. 2-82729. The fastener comprises a plug holder having a base, a plug protuberantly provided on the upper surface of the base, a lever pivotally mounted at its middle on the base and a plate spring acting between one end of the lever and the base and normally urging said one end upward and the other end of the lever down against the base; and a socket having a dent and a resilient engaging rim surrounding the dent, the engaging rim being engageable with the plug of the plug holder. In order to couple the plug holder with the socket, a wearer presses the plug holder against the socket until the plug comes into engagement with the resilient rim of the socket. In order to decouple the plug holder from the socket, he depresses said one end of the lever against the bias of the plate spring whereby the other end of the lever is lifted, thus bringing the plug out of engagement with the engaging rim of the socket.
The first type of conventional fastener suffers from the following drawbacks. In order to couple the plug with the socket, the wearer must forcibly press the plug holder against the socket with the protuberant plug intruding into the hollow cylindrical portion. Since tremendous force is required to forcibly press the plug holder against the socket, the coupling operation is not so easy. Furthermore, all that is necessary for decoupling the plug from the socket is to press the pusher exposed on the outer surface of the socket. So, the pusher can be pushed by the wearer unconsciously or by something extraneous accidentally, so that the plug holder is very likely to come out of engagement with the socket accidentally.
This is also the case with the second type of conventional fastener; that is; since tremendous force is necessary to press the plug holder against the socket the coupling operation is not so easy. Furthermore, all that he must do to decouple the plug holder from the socket is to press one end of the lever which is exposed on the outer surface of the plug holder. So, the lever can be depressed by the wearer unconsciously or mistakenly or by something extraneous accidentally, so that the plug holder comes out of engagement with the socket accidentally.